Method for optionally altering the after-glow period of phosphorescent screens



HI. HINDERER MET HOD FDR OPTIOMLLY ALTERING THE AFTER-GLOW PERIOD OFPHOSPHORESCENT SCREENS Filed NOV. 6, 1936 mwwoflzau aim y grime/14M I 55In the drawing, whereas the photographically non-active ones UNITEDSTATES PATENT orrlce METHOD FOR OPTIONALLY ALTERJNG THE AFTER-GLOWPERIOD or rnosrno- RESCENT SCREENS Heinrich Hinderer, Berlin Zehlendorf,Germany,

assignor to the firm Fernseh Aktien-Gescllschatt, Zehlendorf, nearBerlin, Germany Application November 6, 1936, Serial No. 109,592

' In Germany November 28, 1935 Claims. (Cl. 250--27.5)

The invention relates to a method for option- Figure 1 illustrates Oneform of Cathode my ally altering the after-glow period of phosphotubeadapted for utilizing the method of the inrescent screens, especiallythose used in cathode vention; and y u es. Figure 2 illustratesgraphically the conditions Such optional control of the after-glowperiod occurring in the case of a material selected by 5 is of thegreatest significance when rapidly varyy Of p ing phenomena are to berendered visible or de- Referring to Figure 1, the envelope l houseslmeated, whether it be because the after-glow a c t e 2, a control r ananode 18 entirely undesired or, as occurs in television fleeting plates5 and a phosphorescent Screen 1o practice, because it should havevarying optimum The latter comprises conductive supportin l0 durationdepending on the delineation method means havi g a phosphorescentCoating- A used' heating current is passed through screen 6 fromAttempts have heretofore been made to control source I, and the heatingor polarization is conthe after-glow by suitable choice and mixturetrolled by rheostat of the luminous substance used. It is, however, InFigure 2, the curves indicate the duratio 15 very dimcult to achieve a.perfect result in thi of the after-glow in relation to the temperaturemanner. for the various phosphorescence bands of a It is known that eachphosphorescence band of Zn-S-Mn material. The bands are designated aphosphorescent substance when energized by as usual as a, b and cbands.The after-glow of the light has an upper instantaneous condition. By aband of this phosphorescent material starts at 20 this is meant thetemperature ab v whi h th about +190 0., and the duration of theafterphosphorescence of the band passes into fluoresglow rises verystrongly up to +100". From this cence, that Where it no longer showsaftertemperature on the band after-glows up to --1'70 glowin a strongand continuous manner.

In accordance with the present invention the The blue b band is in itsupper instantaneous p phorescence is entirely or partially convertedcondition even at room temperature; at C. into fluorescence byexcitation by means of it starts to after-glow and at -150 is still verycathode or Roentgen rays, and this is effected prolonged. by heating thephosphorescent material up to The 0 band after-glows at +20" to a veryshort 30 near the corresponding upper instantaneous conextent, and at+50 it ceases. It has its longest 30 dition existing for the cathode orRoentgen ray after-glow at -30 and its lower instantaneous excitation.By suitably choosing the temperacondition at 100. If the phosphorescenceof ture above or below the upper instantaneous conthe 0 band is to beused, the material must be dition, the after-glow may be either entirelysupheated to at least above 50 C., since the upper Dressed or decreasedin a desired manner. instantaneous condition for the 0 band is +50 Theheating of the phosphorescent material to and is room temperature forthe 12 hand. If the the working temperature may be effected byplacmaterial is heated still further, theafter-glow ing the screenmaterial for example on a sheet period of the 0 band may be varied sinceit first of metal, for example of chromium-nickel alloy. passes into theupper instantaneous condition at m which is adapted to be electricallyheated. The +190". In this case the upper limit temperature 40temperature is preferably measured with the aid for the two other bandshas already been exceedof a thermo-element attached to the sheet of ed,that is, they glow no longer. It is thus posmetal as by means of spotwelding. It is also sible, by plotting the operative temperaturepossible to attain the temperature of the upper against the temperatureof the highest upper ininstantaneous condition by heating thephosstantaneous condition, to suppress all of the un- 45 phorescentmaterial by cathode ray bombarddesired bands present in thephosphorescent mament. Furthermore, the temperature of the upterialused. Furthermore, the operative temperaper instantaneous condition canbe attained by ture can be so selected when several bands are preheatingwith the above-described arrangement present that the phosphorescence ofa band is and then first attaining the operative temperatransformed intofluorescence.

ture by the impact of cathode rays. By using the For photographicpurposes, and by suitably secenter of the phosphorescence forfluorescent illecting the temperature, the result can be proluminationpurposes, an increase in instantaneous duced that only allphotographically active bands luminosity may be obtained at the sametime. of the material become free from after-glow,

10 tor the phosphorescent material and this screen may be heatedelectrically or by means of eddy currents in order to bring thephosphorescent material to the necessary working temperature. When anelectrically heated screen is used the screen itself is preferablytraversed by the current.

Admixing the phosphorescent material withconducting particles has alsobeen found to be advantageous in using the method of the inven- 80 tion.

Having thus described my invention, I claim:

1. The method of operating a cathode ray tube having a luminescentscreen which comprises polarizing said screen to a temperature equal to25 the upper limit at which said screen remains phosphorescent, andbombarding said screen with cathode rays to produce a fluorescentresponse.

2. The method of operating a cathode ray tube having a luminescentscreen which comprises polarizing said screen to a temperature equal tothe upper limit at which said screen remains in part phosphorescent, andscanning a modulated cathode ray beam across said screen to produce apartially phosphorescent and partially fluorescent image.

3. The method of operating a cathode ray tube having a luminescentscreen which comprises polarizing said screen to a temperature equal tothe upper limit at which saidscreen remains phosphorescent by means ofunmodulated cathode rays, and directing modulated cathode rays upon saidscreen to produce a fluorescent image.

4. The method of operating a cathode ray tube having a luminescentscreen which comprises polarizing said screen to a temperature equal tothe upper limit at which said screen remains phosphorescent by means ofheating current passing through said screen, and scanning modulatedcathode rays across said screen to produce a fluorescent image.

5. Method of operating a cathode ray tube having a luminescent screen01' Zn-S-Mn material which comprises polarizing said screen to atemperature at which the response at certain colors becomes fluorescent,and bombarding said screen with cathode rays to produce an image.

HEINRICH HINDERER.

